Update: changing the main electrolytic capacitors as well as the tantalum caps around the 7805/7905 voltage regulators did not help. There is still about 600 mVpp of ripple on the +/- 13.9 VDC inputs to the regulators.
Here's a noise measurement on an old second-hand SRS FS710 distribution amplifier. I wonder if the excessive noise at 50 Hz and harmonics is within spec or a result of old age?
Measurement setup: 10MHz signal to a Mini-Circuits ZFSC-2-1+ splitter, one branch to 3120A REF-input, the other branch to the FS710 input, and FS710 output1 to the 3120A DUT input. Noise floor was measured with the same setup but bypassing the FS710.
I measured the CLK2 10 MHz RF-output of two White Rabbit switches with a Microsemi 3120A. The results are similar to previous results with ADEV(1s)=1.5e-11.
When phase-locked to an external reference clock the long-term stability is obviously much better than when free-running, but for small tau, or high offset-frequency in the phase noise plot, the free running oscillator is actually better.